The first paragraph is worded awkwardly, and really needs to be 
clearer.  If for no other reason, this should be done to set a good 
example, since clarity is one of the points of the paragraph.

The subject of the first sentence has three prepositional phrases, which 
is two too many for a subject.  Perhaps "A clear presentation of 
conformance is crucial to the ...."  The reader should surely know at 
this point that conformance, in this document, is shorthand for 
conformance to specification.  If not, then perhaps the second paragraph 
defining conformance should be moved to go first.

The second sentence, while not technically run-on, is too verbose.  "The 
conformance model, its description" is redundant in this context.  In a 
sentence this long, the examples need to be split off into a second 
sentence.  Here's a possible rewording:

   The conformance model and the language used for normative information
   determine the testability of a specification.  They also influence 
the overall
   implementation landscape, ranging from a narrow conformance with few
   allowable variations in implementations to multiple conformance types,
   resulting in numerous conforming implementations.  The model must
   be chosen carefully, to produce the intended implementation range.

In the second paragraph, third sentence, I think "states all the 
criteria" should be replaced with "identifies all the criteria."  A 
reasonable reader should not misinterpret this as implying that nothing 
outside the clause is necessary for conformance.  Nevertheless, even 
reasonable readers may stumble over this, to figure out what it really 
intends.  Even with the suggested change, I don't think this fully 
conveys the idea, but I'm also not sure that's needed.